1. Field of the Invention
The present invention relates to a copying machine which includes a rotary drum housing (referred to as RDH) served as a circulating type subject copy feeding unit for sequentially circulating two or more subject copies (i.e., sheets depicting graphic materials such as pictures, writing, and printing) as those materials being passed an optical scanning point and a sheet refeeding unit for refeeding copying sheets each having a copied image on one side so that the image on one side of the copying material is copied on both sides of each copying sheet.
2. Description of the Related Art
The inventors of the present invention know that there is a copying machine adapted to copy an image formed on one side of a subject copy on both sides of a copying sheet.
The above-mentioned known copying machine includes a RDH which is so arranged that it feeds a subject copy to an optical scan point in a sequentially circulating manner from a final page of subject copies. In a case that the number N of the subject copies is odd, the RDH serves to feed the (N-1) th page of one previous to the final page N and the every other page following the (N-1) th page, that is, (N-1) th page, (N-3) th page, (N-5) th page, . . . , fourth page, and second page (even pages) so that those subject copies are respectively copied on the copying sheets. The copied sheets are temporarily stored in a middle tray. This is a first circulation.
Then, starting a second circulation, the Nth page, that is, the final page is copied on a non-use copying sheet. This non-use copying sheet is ejected to a paper tray. In succession, the copying sheets having a copied image on each one side are fed from the middle tray in a paper-reversed manner so that the remaining pages (N-2) th page, (N-4) th page, . . . , third page, and first page (odd pages) are copied on the non-use sides of those copying sheets. The resulting copying sheets, that is, the sheets having the images on both sides are ejected to a paper tray as disclosed in Japanese Patent Lying-open No. 56-17359.
On the other hand, in a case that the number N of the subject copies is even, during the first circulation, the final page and the every other page following the final page (even pages) are respectively copied on the copying sheets and are stored in the middle tray. In succession, during the second circulation, the (N-1) th page, that is, one previous to the last page and the every other page following the (N-1) th page (odd pages) are copied on the non-use sides of those copying sheets fed from the middle tray and are ejected to the paper tray.
Assuming that the number of the subject copies is five, the foregoing copying process will be described with reference to FIGS. 1 to 9 in more details.
With reference to FIG. 1, the schematic construction of the copying machine 10 will be described. The RDH 11 provides a subject-copy platform 12 on which the subject copies D1, D2, . . . , D5 are laminated in a manner to direct the sides having images I1, I2, . . . , I5 downwardly and to place the final page D5 at the uppermost location.
The subject copies D5, D4, . . . , D1 are fed to a rotary drum 13 through a feeding mechanism (not shown). Those subject copies are reversed through the effect of a reversing mechanism 14 and then are fed to a rotary drum 15. Then, the subject copies are returned to the lowermost location of the subject-copy platform 11 through the effect of the feed-back section (not shown).
Under the RDH 11, a photosensitive drum 16 is located for transferring the images I1, I2, . . . , I5 on the copying sheets P1, P2, . . . , P5. Copying sheets P1, P2, . . . , P5 are fed from a paper cassette 17 to the photosensitive drum 16 through a sheet-feeding belt 18. The copied sheets P1, P2, . . . , P5 are ejected to the paper tray 19 or temporarily stored in the middle tray 20 through the reversing mechanism 21. The reversed sheets P1, P2, . . . , P5 are again fed to the photosensitive drum 16 through a feed-out belt 18.
In copying one side of the subject copy, the light scanning on the subject copy is carried out under the rotary drum 15.
When five subject copies D1, D2, . . . , D5 are copied on both sides of the copying sheets, as shown in FIG. 2, the subject copies are respectively fed to the rotary drum 15 from the final page. The rotary drum 15 is a light scanning place. In this case, no light scanning is carried out on the final page, that is, the fifth page D5. The fifth page D5 is skipped and is returned to the subject-copy platform 12. Then, when the fourth page D4 is passed through the rotary drum 15, the light scanning is carried out on the image I4 so that the image I4 is copied on the first copying sheet P1 fed from the paper cassette 17 (see FIG. 3).
Then, as shown in FIG. 4, the copying sheet P1 is temporarily ejected to the middle tray 20 through the reversing mechanism 21. In the meantime, the third subject copy D3 is skipped without being copied and the image I2 of the second subject copy D2 is copied on the second copying sheet P2.
The first subject copy D1 is skipped without being copied. Next, starting the second circulation, as shown in FIG. 5, the image I5 of the fifth subject copy D5 is copied on the third copying sheet P3 and the resulting third copying sheet P3 is ejected to the paper tray 19 (see FIG. 6).
Then, the feeding of the copying sheets is switched from the paper cassette 17 to the middle tray 20. The first copying sheet P1 is reversed and fed to the photoconductive drum 16 through the effect of the feed-out belt 22. The first copying sheet P1 has the image I4 copied on one side. In the meantime, the fourth subject copy D4 is skipped without being scanned on the rotary drum 15, because the fourth subject copy D4 has been copied. Hence, the third subject copy D3 is guided to the rotary drum 15.
The feeding belt 18 and the feed-out belt 22 are an air absorption type. The time required for switching the air feeding system plus the time required for feeding the copying sheet P1 from the middle tray 20 to the photosensitive drum 16 after being switched is longer than the time required for guiding the third subject copy D3 to the rotary drum 15 after copying the fifth subject copy D5. Hence, as shown in FIG. 6, the subject copy D3 is waiting before the rotary drum 15 while the copying sheet P1 is fed to the photosensitive drum 16.
When the copying sheet P1 is fed from the middle tray 20 to the photosensitive drum 16, as shown in FIG. 7, the image I3 of the subject copy D3 is copied on the non-use side of the copying sheet P1. Then, the resulting copying sheet P1 is ejected to the paper tray 19.
Next, the second copying sheet P2 is fed from the middle tray 20 to the photosensitive drum 16. In the meantime, the second subject copy D2 is skipped without being copied and the first subject copy D1 is guided to the rotary drum 15. And, the image I1 of the subject copy D1 is copied on the non-use side of the copying sheet P2 (see FIG. 8) and the resulting copying sheet P2 is ejected to the paper tray 19. At a time, all the subject copies D5 to D1 are fed back to the subject-copy platform 12 and the double side copying has been done (see FIG. 9).
It will be appreciated from the above description that the double-side copying process consists of copying of the fourth subject copy D4, copying of the second subject copy D2, copying of the fifth subject copy D5, switching of the paper-feeding sources, copying of the third subject copy D3, and copying of the subject first copy D1. While the subject copies D5 to D1 are circulated twice, the overall copying process is completed.
In copying an image formed on each one side of the subject copies by using both sides of the copying sheet, however, the foregoing process requires temporary interrupt of circulating the subject copies when switching the paper-feeding source if the number of the subject copies is odd. It results in disadvantageously making the copying time longer. For example, if the number of the subject copies is 5, as stated above, when the fifth subject copy D5 is copied (see FIG. 5), the paper-feeding source is switched from the paper cassette 17 to the middle tray 20. The switching process needs a considerably long time in switching an air feeding system and feeding the copying sheets from the middle tray 20 to the photosensitive drum 16 after being switched.
Hence, the third subject copy D3 has to wait before the rotary drum 15 until the copying sheet is started to be fed from the middle tray 20.
As depicted in FIGS. 1 to 9, a push-up roller 23 is adapted to push out each of the subject copies from the subject copy platform 12 in sequence.